Electrophotographic-type processes involve a device one of whose components includes a layer of photoconductive insulating material fixed to a conductive backing, termed a "photoconductor". Initially, the surface of the photoconductor is uniformly electrostatically charged over its entire surface, following which it is exposed to a light pattern corresponding to an image to be reproduced. The charge on those surface areas impacted by the light of the image is thereby relatively dissipated, leaving only areas not so impacted in a charged condition. The charge remaining on the surface, therefore, conforms to the configuration of the light pattern reflected from the image to be reproduced.
This latent, electrostatic image can subsequently be "developed" by exposing it to finely divided, electrostatically attractable particulate material. The material is drawn to such surface areas in amounts proportional to the magnitude of the charge in the electrostatically affected areas, thereby forming a temporary image of the material being copied.
The particulate material used to create the temporary image, referred to in the industry as the "toner", typically consists of a pigmented thermoplastic resinous material that can subsequently be transferred to a supporting substrate on which the image of the document being copied is to be permanently fixed. Such a transfer can be accomplished, for example, with the assistance of a corona discharge device that results in the creation of a charge on the substrate, opposite in nature to the charge of the toner forming the temporary image. The temporary toner image is transferred to the substrate by electrostatic attraction occurring when the photoconductor with the image and the substrate are brought into proximity with each other. The transferred image can thereafter be permanently fixed to the substrate by fusing the toner thereto using any of the several known methods.
The process described, depends, however, on the toner being readily available to the charged surface since any deficiencies thereof will result in the charged areas being unable to attract adequate toner. Such an occurrence results in undesirably light images, and therefore in unsatisfactory copies.
Typically, the toner is stored in the copier apparatus in a storage chamber or "toner sump" of a toning station in which the toner is triboelectrically charged in a developer material by mixing. Mixing of the developer material charges and prepares the toner for latent-charge image pickup or removal, as required, thus developing or making such latent image visible. It has been found, however, that the rate of removal of toner from the sump is often erratic and non-uniform. In this regard, and due to their nature and fine particle size, the toner particles have a tendency to pack together, and also to form "bridges", both of which phenomena interfere with the uniform removal of toner from the sump, for example, by a screw conveyor transport system located therein.
In the past, attempts have been made to maintain free flow of the toner material from the sump in a variety of ways, including the use of vibrators attached to the walls of the sump, by various methods of rocking the sump enclosure, by the use of sifting devices, and also through the provision of agitators located within the sump. While some of these expedients have reduced problems of the type referred to, they have been found to entail disadvantages of one kind or another, and non-uniformity of toner withdrawal from the sump has remained a vexing problem.
With respect to agitator devices, for example, they have previously taken the form of wire weldments that are moved within the sump area in an effort to retain the toner particles in a free-flowing condition. Unfortunately, wire forms are often unable to resist the flexing stresses imposed on them during agitation. Furthermore, they have frequently not been able to withstand the bending stresses typically experienced, and are incapable of always successfully resisting the destructive shock forces to which they are continually subjected.